1. Field of the Invention
The present invention generally relates to optical wavelength demultiplexers, and more particularly to a tunable optical wavelength demultiplexer. This application related to a contemporaneously filed application having the same applicants and the same assignee with the invention, and titled xe2x80x9cTUNABLE FILTERED DEVICExe2x80x9d.
2. Description of Prior Art
Optical wavelength demultiplexers have -been commonly used in multi-wavelength optical communications. An optical wavelength demultiplexer can be constructed of a plurality of Bragg gratings connected together. When light with a plurality of wavelengths is incident on such an optical wavelength demultiplexer, light of a first wavelength is reflected by a first Bragg grating, and light at the remaining wavelengths passes through the first Bragg grating and reaches a second Bragg grating, where light of a second wavelength is reflected. Thus, light with a plurality of wavelengths is demultiplexed into a plurality of beams after passing through the optical wavelength demultiplexer, wherein each beam has a different wavelength.
Referring to FIG. 5, U.S. Pat. No. 5,818,986 discloses a conventional optical wavelength demultiplexer 99 which includes a plurality of Bragg gratings 901, 902, 903 located in a planar waveguide 91. Dots 904 indicate unshown Bragg gratings located between the Bragg gratings 902, 903. Light 914 at a plurality of wavelengths xcex1, xcex2, to xcexN is received at an input port and passes through a channel 911 to be incident on the first Bragg grating 901 at a predeterminated acute angle. Light 915 at a particular wavelength xcex1 is reflected by the first Bragg grating 901 to a channel 921 and is output through a first output port. Light at the remainder wavelengths passes through the first Bragg grating 901 and is incident on the second Bragg grating 902. In a similar process, the remainder wavelengths from the first Bragg grating 901 are successively split into a plurality of beams at a plurality of Bragg gratings, each beam having a particular wavelength. The wavelength of each reflected beam is determined by properties of Bragg grating which reflects the beam.
However, the convention optical wavelength demultiplexer has a shortcoming. That is, the demultiplexed wavelengths of output light are fixed when the optical wavelength demultiplexer is manufactured.
Therefore, an improved optical wavelength demultiplexer which has the demultiplexed wavelengths of output light tunable is desired to overcome the shortcoming of the prior art.
Accordingly, an object of the present invention is to provide a tunable optical wavelength demultiplexer.
To achieve the above-mentioned object, a tunable optical wavelength demultiplexer in accordance with the present invention includes a plurality of demultiplexer units formed in a planar waveguide. Every demultiplexer unit comprises a plurality of input waveguide channels, a plurality of output waveguide channels and a Bragg grating. Every input waveguide channel angularly merges at a different acute angle with a normal of the Bragg grating, and every output waveguide channel is a mirror image of every input waveguide channel. The Bragg grating of every demultiplexer unit has a different period, input waveguide channels of every demultiplexer unit can receive light from corresponding input waveguide channels of the previous demultiplexer unit.